1. Field of the Invention
The present invention relates to alarm systems, and particularly to heat sensing systems which are designed to give early warning of a fire before it has progressed to a major blaze.
2. Brief Description of the Prior Art
Every year, in cities and communities across the nation, fire catastrophes cause countless losses of life and property. For example, in the United States fire is the largest single cause of injuries in hotels and motels, 36% of such injuries being caused by smoking in bed. Not counted in such statistics in the untold pain and suffering of those injured in residential and commercial fires. Such statistics cannot begin to reflect the terrible anguish born by these and others not only over the loss of their cherished possessions, but even more over the sufferings and losses of their friends and loved ones.
As technology progresses, and as the public more and more accepts the fact that we all share a common risk and exposure to these sudden and unexpected losses, countermeasures have become increasingly evident. For example, building codes in more and more communities are requiring public buildings, nursing homes, hotels, motels, and so forth to install and maintain smoke detectors and sprinkler systems, to use fire retardant materials, and so on. More and more homeowners are installing smoke detectors in their homes to give early warning of a fire. More expensive residential systems will even transmit an alarm directly to the local authorities when a fire or smoke is detected.
Unfortunately, most such systems are as expensive as they are sophisticated. Their use is therefore restricted to those who can afford them, and even then to only those applications which their users consider to be "cost effective". Additionally, such systems, notwithstanding their sophistication, are often woefully deficient in furnishing the earliest possible warning in certain types of fires. For example, one of the most tragic fires is the mattress fire caused by a smoker who falls asleep while smoking in bed. Such a person can suffer serious body burns (not to speak of the dangers from the smoke and fumes generated by the smoldering mattress fire) long before a conventional smoke or fire detector will respond.
Other examples where inexpensive, versatile detectors would be especially useful include: detecting imminent spontaneous combustion due to unfavorable temperature conditions, as in a closed area; monitoring the condition of goods subject to heat damage during transit and sounding an immediate alarm upon an unfavorable temperature condition, rather than simply activating a tell-tale warning tag which is usually discovered much later after the damage has progressed too far to be corrected; and so forth. Such needs often go unanswered because presently available detectors are simply too expensive for mass use in statistically low-risk situations.
A need thus remains for an inexpensive, uncomplicated, versatile and reliable fire alarm system and method which will give the earliest possible warning of a fire hazard. Preferably such a system and method can be configured to give a warning long before temperatures rise to the point of combustion. In some cases, such as detecting a mattress fire, the warning should be given long before the temperature rises to that of a cigarette, 125020 F. Desirably, such a system and method would lend itself readily to economical use in virtually any environment or application where early and reliable detection of an undesirably high temperature is needed.
The following patents illustrate various prior art concepts having some relevance to this invention:
Girogianni U.S. Pat. No. 2,488,622, issued Nov. 22, 1949, discloses a flash bulb in parallel with a normally closed circuit which fires if the other circuit is broken.
Margulies U.S. Pat. No. 3,158,713, issued Nov. 24, 1964 discloses a latching indicator to indicate an open electrical circuit, such as a blown fuse.
Shiraishi U.S. Pat. No. 3,210,751, issued Oct. 5, 1965, discloses a circuit which requires only a small amount of electricity to monitor a closed loop circuit and actuate an alarm if the loop circuit is broken.
Morreal et al. U.S. Pat. No. 3,367,175, issued Feb. 6, 1968, discloses an ablation sensor containing embedded wires which form a plurality of electrical circuits as they erode, melt, or ablate along with the material on which the wires are supported. Opening of the normally closed circuits thus results, not from fracturing of the conductor caused by thermally induced melting and migration of the adhering substrate material, but by melting and evaporation of the conductor when the adjacent substrate ablates. The "break" in the conductor thus results from erosion, not from physical migration of an underlying substrate.
Leslie U.S. Pat. No. 3,510,762, issued May 5, 1970, discloses a temperature monitoring device composed of a high frequency cable having a temperature sensitive dielectric. When the dielectric changes state at a certain location (melts or vaporizes), the impedance of the cable thereat changes, and the location can be detected by standard pulse echo techniques.
Simon et al. U.S. Pat. No. 3,595,228, issued July 27, 1971, discloses an electric alarm device for detecting a break in a releasable flow line coupling, such as a respirator.
Lewis U.S. Pat. No. 3,813,662, issued May 28, 1974, discloses an alarm system, which detects both open-circuiting of a loop and effective short-circuiting of the loop rectifier element.
Banner U.S. Pat. No. 3,898,641, issued Aug. 5, 1975, discloses a security rope containing wires coupled to a boat mooring bit such that an alarm is set off when the rope circuit is disturbed.
Cooke U.S. Pat. No. 4,288,425, issued Oct. 14, 1980, discloses a wire-containing alarm glass plate laminated to a plastic layer of polyvinyl butyral which becomes opaque upon breakage.
Clark et al. U.S. Pat. No. 4,236,146, issued Nov. 25, 1980, discloses a switchless circuit for constantly and simultaneously monitoring both open and closed circuits.
Lewiner et al. U.S. Pat. No. 4,263,589, issued Apr. 21, 1981, discloses an electromechanical device for detecting a break in a DC circuit.
Domingue (applicant herein) U.S. Pat. No. 4,520,352, issued May 28, 1985, discloses the concept of a fire alarm system and method in which the heat sensor comprises a continuous wire secured to or laminated or sandwiched between one or more sheets or films of heat migratable plastic whereby the application of heat on a localized basis, as in the case of a cigarette dropped on a bed, or on a more generalized basis, as in the case of an entire room or zone being brought to a somewhat elevated temperature, causes the plastic to shrink and break the wire, or allow the wire to separate by melting, to set off the associated alarm.
Japanese Pat. No. 144699 discloses another form of fire alarm system utilizing a heat shrinking plastic sheet or film for breaking an alarm wire.